Superlattices with scattering mechanisms at multiple length scales efficiently scatter phonons at all relevant wavelengths and provide a convenient route to reduce thermal transport. Here, we show, both experimentally and by atomistic simulations, that SiGe superlattices with well-established compositional gradients and a sufficient number of interfaces exhibit extremely low thermal conductivity.
Our results reveal that the thermal conductivity of long-period (30–50 nm) superlattices with thicknesses below 200 nm is still thickness-dependent and higher than that of the corresponding alloy thin film. Increasing the number of periods up to 16 has a strong impact on heat propagation, leading to thermal conductivity values below the thin-film alloy limit. Lattice dynamics calculations confirm that the reduced thermal conductivity stems from the simultaneous effects of mass scattering, graded interface scattering, and coherent interference from the lattice periodicity. This study provides a significant step forward in understanding the role of compositional gradients in heat transport across nanostructures. The strategy of employing long-period graded superlattices with extremely low thermal conductivities has great potential for micro- and nano-thermoelectric generation and cooling of Si-based devices.
Sustainable energy conversion & storage systems
Beating the Thermal Conductivity Alloy Limit Using Long-Period Compositionally Graded Si1–xGex Superlattices
P. Ferrando-Villalba, Shunda Chen, A. F. Lopeandía, F. X. Alvarez, M. I. Alonso, M. Garriga, J. Santiso, G. Garcia, A. R. Goñi, D. Donadio*, and J. Rodríguez-Viejo*
The discovery of novel high-performing materials such as non-fullerene acceptors and low band gap donor polymers underlines the steady increase of record efficiencies in organic solar cells witnessed during the past years. Nowadays, the resulting catalogue of organic photovoltaic materials is becoming unaffordably vast to be evaluated following classical experimentation methodologies: their requirements in terms of human workforce time and resources are prohibitively high, which slows momentum to the evolution of the organic photovoltaic technology.
Major research efforts are being carried out for the technological advancement to an energetically sustainable society. However, for the full commercial integration of electrochemical energy storage devices, not only materials with higher performance should be designed and manufactured but also more competitive production techniques need to be developed.
Recently synthesized hexagonal group IV materials are a promising platform to realize efficient light emission that is closely integrated with electronics. A high crystal quality is essential to assess the intrinsic electronic and optical properties of these materials unaffected by structural defects. Here, we identify a previously unknown partial planar defect in materials with a type I3 basal stacking fault and investigate its structural and electronic properties.
The advanced materials industry is one of the leading technology sectors worldwide. The development of such materials is at the core of the technological innovations and has been possible in the last century thanks to the transition from “observational” science to “control” science.
Transition metal carbides have gathered increasing attention in energy and electrochemistry applications, mainly due to their high structural and physicochemical properties. Their high refractory properties have made them an ideal candidate coating technology and more recently their electronic similarity to the platinum group has expanded their use to energy and catalysis. Here, we demonstrate that the nanostructuring and stoichiometry control of the highest melting point material to this date (Ta-Hf-C) results in outstanding electrochemical stability.